Description of the Related Art
The present invention relates to a method of forming a semiconductor device, and more particularly to a method of forming a metal plug buried in an insulation layer over a semiconductor substrate and an interconnection extending over the insulation layer so as to be connected to the metal plug.
One of the conventional methods for forming the buried metal plug and the interconnection is disclosed in Japanese laid-open patent publication No. 5-275366. A conductive plug is buried in the insulation film before a top portion of the conductive plug and a top surface of the insulation film are planerized for subsequent formation of an interconnection layer extending over the planarized surface of the insulation film.
The above method will be described in detail with reference to FIGS. 1A through 1D. With reference to FIG. 1A, an insulation film 2A is formed on a top surface of a semiconductor substrate 1. A contact hole 3 is formed in the insulation film 2A. A tungsten film 7 is deposited by a chemical vapor deposition over the insulation film 2A and within the contact hole 3 so that the tungsten film 7 within the contact hole 3 is in contact with the semiconductor substrate 1. With reference to FIG. 1B, a first chemical mechanical polishing method is made wherein a polishing rate of the tungsten film 7 is much higher than a polishing rate of the insulation film 2A so that the tungsten film 7 over the insulation film 2A is removed and a surface region of the insulation film 2A is also removed as well as the tungsten film 7 within the top portion of the contact hole 3 is further removed. As a result, an overpolishing of the tungsten film 7 within the top portion of the contact hole 3 appears to form a recess 8 at the top portion of the contact hole 3. The top portion of the remaining tungsten plug 7A within the contact hole 3 is leveled slightly lower than the top surface of the insulation film 2A.
With reference to FIG. 1C, a second chemical and mechanical polishing is made wherein a polishing rate of the tungsten film 7 is much lower than a polishing rate of the insulation film 2A so that mainly the surface region of the insulation film 2A is polished whereby the top surface of the insulation film 2A is leveled to the top portion of the tungsten plug 7A.
With reference to FIG. 1D, an interconnection layer 9 is entirely deposited on a leveled or planarized surface of the insulation film 2A with the tungsten plug 7A. The interconnection layer 9 is then patterned to form an interconnection which is in contact with the top portion of the tungsten plug.
The above conventional method has the following three problems.
First, in order to level the top portion of the tungsten plug to the insulation film 2A, two chemical and mechanical polishing processes are required as described above. This makes the fabrication process complicated.
Second, the tungsten plug and the interconnection layer are formed by two deposition processes and two chemical and mechanical polishing processes in separate processes as described above. This makes the fabrication process complicated.
Third, the increase in resistance of the connection portion between the tungsten plug and the interconnection or any disconnection between the tungsten plug and the interconnection may be caused because the tungsten plug and the interconnection layer are deposited in separate processes as described above.
In the above circumstances, it had been required to develop a novel method of forming a buried plug and an interconnection over the same free from the above three problems.